Use a hash table to improve the preformance of column name uniqueness checking.

FossilOrigin-Name: 5b08f29f458c600401860c7d70d8174cf61e69f8

1 files changed, 18 insertions, 20 deletions

diff --git a/src/select.c b/src/select.c
index afebf87ba..802e75eec 100644
--- a/src/select.c
+++ b/src/select.c
@@ -1602,7 +1602,9 @@ int sqlite3ColumnsFromExprList(
   Expr *p;                    /* Expression for a single result column */
   char *zName;                /* Column name */
   int nName;                  /* Size of name in zName[] */
+  Hash ht;                    /* Hash table of column names */
 
+  sqlite3HashInit(&ht);
   if( pEList ){
     nCol = pEList->nExpr;
     aCol = sqlite3DbMallocZero(db, sizeof(aCol[0])*nCol);
@@ -1614,7 +1616,7 @@ int sqlite3ColumnsFromExprList(
   *pnCol = nCol;
   *paCol = aCol;
 
-  for(i=0, pCol=aCol; i<nCol; i++, pCol++){
+  for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
     /* Get an appropriate name for the column
     */
     p = sqlite3ExprSkipCollate(pEList->a[i].pExpr);
@@ -1643,32 +1645,28 @@ int sqlite3ColumnsFromExprList(
         zName = sqlite3MPrintf(db, "%s", pEList->a[i].zSpan);
       }
     }
-    if( db->mallocFailed ){
-      sqlite3DbFree(db, zName);
-      break;
-    }
 
     /* Make sure the column name is unique.  If the name is not unique,
     ** append an integer to the name so that it becomes unique.
     */
-    nName = sqlite3Strlen30(zName);
-    for(j=cnt=0; j<i; j++){
-      if( sqlite3StrICmp(aCol[j].zName, zName)==0 ){
-        char *zNewName;
-        int k;
-        for(k=nName-1; k>1 && sqlite3Isdigit(zName[k]); k--){}
-        if( k>=0 && zName[k]==':' ) nName = k;
-        zName[nName] = 0;
-        zNewName = sqlite3MPrintf(db, "%s:%u", zName, ++cnt);
-        sqlite3DbFree(db, zName);
-        zName = zNewName;
-        j = -1;
-        if( zName==0 ) break;
-        if( cnt>3 ) sqlite3_randomness(sizeof(cnt), &cnt);
-      }
+    cnt = 0;
+    while( zName && sqlite3HashFind(&ht, zName)!=0 ){
+      char *zNewName;
+      nName = sqlite3Strlen30(zName);
+      for(j=nName-1; j>0 && sqlite3Isdigit(zName[j]); j--){}
+      if( zName[j]==':' ) nName = j;
+      zName[nName] = 0;
+      zNewName = sqlite3MPrintf(db, "%s:%u", zName, ++cnt);
+      sqlite3DbFree(db, zName);
+      zName = zNewName;
+      if( cnt>3 ) sqlite3_randomness(sizeof(cnt), &cnt);
     }
     pCol->zName = zName;
+    if( zName && sqlite3HashInsert(&ht, zName, pCol)==pCol ){
+      db->mallocFailed = 1;
+    }
   }
+  sqlite3HashClear(&ht);
   if( db->mallocFailed ){
     for(j=0; j<i; j++){
       sqlite3DbFree(db, aCol[j].zName);